shifts the value in the most significant byte in the counter register 8 bits to the left, which is typically done as

Code ( (Unknown Language)):

TMR0H<<8

, but that's not important...
The shift is needed because the counter is 16 bits, but the registers are 8 bits wide, so you shift the most significant byte into position and add the least significant byte.

Since this count is over the period of

Code ( (Unknown Language)):

Delay_ms(1000); // Wait for 1 sec

this gives us counts per second. Multiplying by 60 gives counts per hour.